Directive antenna system



SEARCH RDQM Nov. 30, 1954 w. D. LEWIS omcnvs ANTENNA SYSTEM 5Sheets-Sheet 1 Filed July 31, 1944 FIG.

Since-- INVENTOR n10. LEW/S ATTORNEY 5 Sheets-Sheet 2 Filed July 31,1944 INVENTOR n. 0. 1. EW/S ATTORNEY Nov. 30, 1954 w. o. LEWIS DIRECTIVEANTENNA SYSTEM 5 Sheets-Sheet 3 Filed July 31, 1944 INVENTOR W 0. L EWIS ATTORNEY Nov. 30, 1954 w. o. LEWIS DIRECTIVE ANTENNA SYSTEM 5Sheets-Sheet 4 Filed July 31, 1944 Nov. 30, 1954 w. D. LEWIS 2,695,958

DIRECTIVE ANTENNA SYSTEM Filed July 31, 1944 5 Sheets-Sheet 5 ATTORNEYgain, in a sense oppose each other.

United States Patent 0 DIRECTIVE ANTENNA SYSTEM Willard D. Lewis, LittleSilver, N. J., assignor to Bell Telephone Laboratories. Incorporated,New York. N. Y., a corporation of New York Application July 31, 1944,Serial No. 547,396

10 Claims. (Cl. 250-3365) This invention relates to antenna systems andparticularly to directive antenna systems.

As is known, antenna systems comprising a conventional oscillating orrocking parabolic reflector and a primary antenna member positioned atthe focus, and

systems comprising a stationary parabolic reflector and a primaryantenna movable through or about the focus, have been suggested for usein radar systems of the scanning type. Also parabolic reflectorsassociated with a pair of alternately energized primary antennasdisplaced equally from the focus have been used in radar systems of thelobe switching type. In the scanning arrangements utilizing parabolicreflectors the three requirements of rapid scan, wide scanning angle andhigh For example, the gain is proportional to the size of the reflectoraperture or diameter as measured in wavelengths. More specifically, therocking reflector system is not always completely satisfactory because,assuming a large reflector aperture is used in order to secure a highgain. the large aperture prohibits rapid movement of the reflector. Inthe prior art scanning systems utilizing a conventional passive member,such as a parabolic reflector, and a primary antenna moving through thefocus, while a fairly narrow beam or major lobe is secured with theprimary antenna at the focus, the lobe widens, the gain decreases andthe minor lobes become pronounced as the spacing between the focus andthe primary antenna increases. In fact. when the primary antenna isdisplaced an amount suflicient to align the lobe axis with the extremeangular directions in the scanning sector, as in a wide scan system, thelobe often becomes bifurcated whereby ambiguous scanning obtains. As aresult, scanning by means of a moving primary antenna has beensatisfactorily achieved over only a relatively small angle or sector.Accordingly, it now appears desirable to secure a high gain system whichpermits rapid wide angle scanning.

It is one object of this invention to obtain, in an antenna system asteerable major lobe pattern the width of which remains substantiallyconstant during movement of the lobe.

It is another object of this invention to secure, in an antenna systemcomprising a passive member having a focus and a primary antenna memberdisplaced in a given plane from the focus, a directive pattern in saidplane which is substantially the same as that obtainable in theaforementioned plane with a primary antenna at the focus.

It is a further object of this invention to secure in a radar antennasystem comprising a reflective member having a focal point and a primaryantenna moving about the focal point, a major lobe pattern in each planecontaining the reflector axis which is substantially the same as thatobtainable in said plane with the primary antenna at the focal point.

lt is still another object of this invention to obtain. in a radarantenna system comprising a cylindrical parabolic reflector and aprimary antenna oscillating along the latus rectum of the reflector,optimum scanning over a wide angular sector in the plane of oscillationof the primary antenna.

As used herein, the term focus is generic to focal point and focal lineor linear focus; the term phase refers to phase angle" and not topolaritythe term propagation" is generic to reception" and emission ortransmission"; and the term conic is generic to "parabola," ellipse andhyperbola.

In accordance with one embodiment of the invention the antenna systemcomprises a plurality of coaxial, confocal cylindrical parabolic zonereflectors or annular facets having focal lengths which ditfer ahalf-wavelength or a multiple thereof. The corresponding segmentalportions, such as the approximate mid-points, of the zones are locatedon the circumference of an intermediate" circle having its center on thecommon focal line of the zones. The outer edges of the zones lie on thecircumference of an outer circle and the inner edges are positioned onthe circumference of an inner circle, the three circles being concentricand the outer and inner circles having radii which differ preferably,but not necessarily, a half-Wavelength. Considering any pair ofintermediate adjacent parabolic zones and assuming the reflectorcomprises a large number of zones, the adjacent zone boundaries areconnected together by plane non-reflective members extending parallel tothe common axis of the zones. If the reflector comprises only a fewzones the non-reflective members preferably extend along radii of theouter circle, the outside edge of each member being connected to theedge of the adjacent inner zone and the inside edge being connected tothe edge of the outer zone by an elliptical reflector. One focus of theelliptical reflector is at the common focus of the parabolic zones andthe other focus is at the edge of the inner zone.

A primary transceiving antenna member, such as a wave guide aperture, ispositioned substantially in the common focal plane of the zones, and atranslation device is connected to the primary antenna. Means areprovided for oscillating the primary antenna along a substantiallylinear path aligned in part with the common latus rectum of the zonesand having its mid-point superimposed on the common center of theaforementioned circles. The maximum displacement of the primary antenna,corresponding to one-half of the linear path, is relatively small ascompared to the radius of the intermediate circle. In a modification,the path of oscillation is circular. Also, if desired, means forswitching the primary antenna between two positions displaced from thefocus may be used in place of the means for oscillating the primaryantenna.

In transmission, wave components emitted by the primary antenna impingeon the zones and each zone taken by itself functions as a. conventionalparabolic reflector associated with an on-focus primary antenna.Considering any pair of zones, the components are reflected in the samedirection for a given position, on or off the focus, of the primaryantenna since the zones are positioned on the circumference of a circle.The angle a between the common direction of maximum radio action for agiven position of the primary antenna and the common zone axis isdependent upon the position or displacement of the primary antenna and,if the displacement is zero, the common direction of action and thecommon zone axis are coincident. In addition, assuming for the momentthat the primary antenna is at the focus, the wavelets propagated viaall zones in a direction coincident with the common zone axis, andhereinafter termed the on-axis or axial direction, combine in phaseagreement, inasmuch as the focal length of the two zones differ ahalf-wavelength or any multiple thereof. Stated differently, for thecondition just assumed, the wavelets produce a plane wave front parallelto the latus rectum. Also, by reason of fire aforementioned differencesin the zone focal lengths, the wavelets combine to produce a wave front,which is substantially plane and perpendicular to the off-axis directionwhen the primary antenna is displaced from the focus and the axis of themajor lobe of the system is aligned with an off-axis direction. Theelliptical reflector functions to eliminate the small aberration orso-called edge effect produced at the inner edge of each intermediatezone.

In accordance with another embodiment of the invention, the antennacomprises coaxial paraboloidal zones having a common focal point andmeans for moving the primary antenna along a linear path containing thefocal point, or means for moving the primary antenna about the focalpoint and along a curvilinear path such as a circular or ellipticalpath. In this embodiment the approximate mid-points of the zones arespaced on the surface of a sphere having its center on the common focalpoint. If the reflector comprises a large number of zones the adjacentzones are preferably connected by means of non-reflective memberscorresponding to sections of right cylinders having a common axis anddifferent diameters. If the reflector includes a large number of zonesthe adjacent zones are connected by two contiguous members, one of whichis aligned with the radius of the sphere and is shaped like a truncatedcone. the other of which corresponds to a surface of. revolution formedby rotating a section of an ellipse about its focus at the center of thesphere.

The invention will be more fully understood from a perusal of thefollowing specification taken in conjunction with the drawings on whichlike reference characters denote elements of similar function, and onwhich:

Figs. 1 and 2 are diagrams used for explaining the invention;

Fig. 3 is a diagrammatic sectional view of one embodiment of theinvention;

Fig. 4 is a diagrammatic sectional view of another embodiment of theinvention;

Fig. 5 is a perspective view of a reflector constructed in accordancewith the invention and comprising paraboloidal zones;

Fig. 6 is a perspective view of a reflector constructed in accordancewith the invention and comprising cylindrical parabolic zones;

Fig. 7 is a sectional view of a zoned parabolic reflector comprising alarge number of zones; and

Figs. 8, 9 and 10 illustrate measured directive curves for the system ofFig. 7.

Referring to the two-dimension diagram of Fig. I, reference numeral 1denotes a curve of the equation where, in polar coordinates r is theradius vector and 6 the vectoral angle. Reference numeral 2 denotes thepole or origin having the rectangular coordinates o, and numerals 3 and4 denote, respectively, the XX or polar axis and the YY axis. Numeraldesignates the position of a primary antenna or a source which movesalong the YY axis. The position 5 has the rectangular coordinates o, y.Now by design so that the distance de from the source 5 to point 6 oncurve 1 is, as shown in Fig. 1, approximately equal to r-y sin 6 (3) andthe distance di from source 5 to point 7 on curve 1 is approximatelyequal to r+y sin 9 (4) Hence,

cophasal for the propagation direction which is perpendicular to thewave front 9 and forms with the XX axis an angle a. whose sine is equalto 2y sin 0 y 21' sin 0 r (6) It may be noted by way of explanation thatif the reflector corresponding to curve 1 were a conventional parabolicreflector, and if the source 5 were at the focus or origin 2, the radiusvector r would vary and wavelets reflected by its various elementalreflector portions would be cophasal for the single direction coincidentwith the XX axis. Hence a narrow major lobe would be secured. With thesource displaced from the origin 2, however, certain wavelets reflectedby the hypothetical parabolic reflector completely reinforce or agree inphase for several directions and a wide major lobe is obtained. Thewidth of the lobe is related to the displacement of the source and,assuming the source moves along the YY axis, the lobe width varies asthe source moves. Also, if the reflector were circular the center of thecircle being at 2. that is, if r is made equal to a constant, the twowavelets reflected by every pair of segments, such as 6 and 7, would becophasal for direction 10, but the wavelets reflected by the varioussets or pairs of segments would not be in phase. In accordance with theinvention, the segments or zones of the reflector are, considering the xand y planes and disregarding for the moment the 1, plane, (1) arrangedon the circumference of a circle having a radius vector r equal to aconstant k, whereby the wavelets reflected by each pair of correspondingzones combine in phase for the single direction 10 when the source is at0, y. The equation for the circle is +y As shown below, the segments orzones comprise coaxial confocal parabolic sections whereby, with thesource at the focus 2, the wavelets are in exact phase agreement fordirection 10. With the source displaced from the focus as, for exampleat 5, the wavelets are in substantial phase agreement for the principaldirection of action, for example, direction 10. Accordingly, in theplane containing the reflector axis and the linear path traversed by thesource, the zones should be arranged on the circumference of a circlehaving its center at the intersection of the reflector axis and thepath.

Referring to the three dimension diagram of Fig. 2, it will now be shownthat, considered in the solid, the zones should lie on the surface ofsphere having its center at the aforementioned intersection or focus.Reference numeral 12 denotes a reflector having its axis aligned withthe XX axis, a vertex 13 at point v, o, 0, and a focal plane parallel tothe YZ plane. With the primary antenna at the origin 14, the major lobeor beam is, as shown by arrow 15, parallel with the XX axis and the wavefront 16 is perpendicular to the XX axis. Numeral 17 denotes anelemental reflector portion having the coordinates x, y and z and spaceda distance r1 from the origin 14. Now if the primary antenna is moved tothe point or position 18 having the coordinates 0, yz, 0 and spaced adistance r2 from the segment 17, the axis 19 of the major lobe makes anangle with the XX axis and the wave front 20 forms an angle P with thewave front 16. The difference D in distance, r1r2, represents the changein phase angle of the energy at the reflector, which change produces thebeam shift. By design y2 r1 The distance r1 is given by the followingequation '1 l +yl 1 and the change or difference D in distance is 1=T.T.=-WT.=

Expanding the binomial, we get is less than 1, so that all termscontaining ya, or higher powers of yz, may be neglected.

Hence,

But, since all parts of reflector 12 are to contribute cophasal waveletsin direction 17, the change D should be y sin Q (16) r1 Sin (I) aconstant In other words, the segments or zones of the reflector shouldlie on a sphere.

Referring to Fig. 3 reference numeral 21 denotes a zoned reflectorcomprising the three parabolic zones 22. 23 and 24 which have a commonaxis 25, a common focus 26 and a common latus rectum 27. The zones maybe sections of cylindrical parabolic reflectors or paraboloidalreflectors. Reference numerals 28 denote the outer edges of the zones22, 23 and 24 and numerals 29 designate the inner edges of zones 23 and24 and the vertex of the inner zone 22. Numerals 3t) denotecorrespondent intermediate points or elemental portions of the zones.The zones are positioned so that the corresponding intermediate points30 lie on the circumference of an intermediate circle 31. edges orpoints 28 lie on the circumference of an inner circle 32 and the innerpoints 29 on the circumference of an outer circle 33, the three circles31, 32 and 33 being concentric with the common center at the commonfocus 26. The inner zone 22, the intermediate zone 23 and the outer zone24 have focal lengths of a 2, a?\ and respectively, where a is theradius of the outer circle 33 and A is the mean operating or designfrequency. Preferably, but not necessarily, the inner and outer circles32 and 33 have radii differing a half-wavelength, or an odd multiplethereof, whereby the outer edge 28 of zone 23 and the inner edge 29 ofzone 24 lie on one line parallel to axis and the inner edge 29 of zone23 and the outer edge of zone 22 lie .on another line parallel to theaxis. Expressed mathematically the equation for where n is any oddinteger. Now the equation, as given on page 78 of the textbook AnalyticGeometry by W. A. Wilson and J. I. Tracey, for a parabola having .itsaxis aligned with the XX axis 25 and its vertex at the origin is asfollows:

where p is the distance between the directrix and the latus rectum andis equal to twice the distance between the vertex and the latus rectum.If in Fig. 3 the origin is taken at the vertex of any of the zones, wehave and 3 y=4 a-n$ :c (22) where n is an odd integer. With the origintransformed to the focus 26 we have Hence the zoned reflector comprisesparabolic zones which lie between the circles corresponding to Equations17 and 19 and each of which is represented by Equation 23. If the zonesare numbered 1, 2, 3, etc., beginning with the central zone 22, thecoordinates for the point The outer coincident with the outer edge ofthe mth zone, where m is the zone number, are determined by the equationY= 2k; --mx 1iX 24 and the coordinates for the point coincident with theinner edge are determined by the equations The edges 28 and 29 of zone23 are connected to the adjacent edges of zones 22 and 24 by thenon-reflective members 34. If the zones 22, 23 and 24 are paraboliccylinders four separate members 34 are employed, each member being flatand rectangular; and if the zones have paraboloidal surfaces a singlemember in the form of a tubular right cylinder connects zones 22 and 23and another hollow cylindrical member coaxial with the firstmentionedtubular member connects zones 23 and 24.

Reference numeral 35 designates a primary antenna member such as a hornor a waveguide aperture which is connected to a transceiver and which ismovable along the latus rectum path 36 and between the limiting points37 and 38. The horn is designed so as to produce a properly taperedillumination of the reflector. The electric polarization of the wavestransmitted and received by the primary antenna is linear, the directionof polarization being, for example, vertical.

In operation, assuming for the moment that primary antenna is at thefocus 26, waves emitted by the primary antenna 35 and having a sphericalwave front are reflected by zones 22, 23 and 24. The reflected waveletsare cophasal in direction 39, since the lengths of the paths 40, 41 and42 from the focus 26 to the latus rectum plane 27 via zones 22, 23 and24 differ from each other a wavelength or a multiple thereof. Thewavelets impinging upon the electrically transparent connecting members34 are not reflected. With the primary antenna at position 38 and spaceda distance Dss from the focus 26, the wavelets reflected at thecorrespondent intermediate segments 30 combine in phase angle agreementfor the single direction 43, as indicated by the plane wave front 44.The direction 43 makes with the axis 25 an angle -ct30 whose sine isfrom Equation 6, equal to the ratio of the displacement Das to theradius r of circle 31, t at is,

and the wavelets reflected by the elemental outer edge portions 28combine in phase agreement for a single direction 46 making with theaxis 25 a slightly larger angle a29 whose sine is The phase angles ofthe wavelets arriving at the Wave front 44 from segments 28, 29 and 30are slightly different so that the wave front is slightly curved ratherthan flat. The differences in angles or directions -ocas, a:9 and a3oand the phase angle differences for these angular directions are,however, negligible and such that a substantially plane wave frontperpendicular to. the mean direction 43 is secured.

Considered more broadly, with the primary antenna at position 38, eachparabolic zone considered by itself functions as a conventionalparabolic reflector of the prior art. If zones 22, 23, 24 were modifiedand included in the same parabolic surface, that is, if a conventionalparabolic reflector such as represented by the curve 47 were employed,the difference or angle between the directions traversed by the waveletsreflected from the outer edge 28 and the inner edge or vertex portion29, and the corresponding phase angle difference, would be relativelylarge whereby a low gain, a broad major lobe and pronounced minor lobeswould be secured. By utilizing for each zone a small parabolic section,the angle between the directions traversed by the wavelets reflectedfrom the inner and outer edges of each zone, and the corresponding phaseangle difference, are rendered small. By off-setting the zones so thatcorresponding segments lie on the circumference of the same circle thewavelets reflected from the corresponding segments, equally distant fromthe axis X, X, of Fig. I. agree in phase and direction, or stateddifferently, the radiations from the several zones are superimposed andreinforced to achieve a maximum effect in substantially a singledirection. Moreover, by reason of the zoning.

the primary antenna may be displaced from t..e focus a greater distancewithout materially widening the lobe than is permisstble in prior artsystems using a conventtonal parabolic reflector. Accordingly, by virtueof the zoning, a scanning sector of greater angular width is obtained ascompared to the sectors in prior art systems.

As the primary antenna moves from the positive position 38 towards thefocus 26 the angles a,,,, a and a,,, become smaller, and with theprimary antenna on the negative side of the axis 25 the angles becomepositive, the position of the major lobe axis being a function of thesign and amount of the displacement of the primary antenna. As theprimary antenna moves from the positive extreme position 38 through thefocus 26 to the negative extreme position 37 the width of the major lobechanges only slightly since the difference in the angles or directions aand 0: is zero for the focal position 26 ang 3relatively small for eachof the extreme positions 38 an 7.

In reception the converse operation obtains by reason I called edgeeffect may be partially compensated by interposing an ellipticalmetallic member between each pair of adjacent zones. In Fig. 4 referencenumeral 48 denotes non-metallic members which extend from the inner edge29 of zones 23 and 24 outwardly along the radii 49 and of circle 32.Numerals 51 and 52 denote elliptical metallic members connecting theouter edges 28 of zones 22 and 23 to the outer edges of the planemembers 48. The elliptical members 51 and 52 each have an axis alignedwith, and a pair of foci on, the radii 49 and 50 respectively, one ofthe foci being at the common parabolic focus 26 and the other at thezone edge 29 on its axis. Since the spacings between the adjacent points28 and 29 differ, the members 51 and 52 have different ellipticalcurvature. In the case of each elliptical member the ellipse may bereadily determined since the two foci and the point 28 on the ellipseare known.

The system of Fig. 4 operates in the same manner as the system of Fig. 3except that the wavelets emitted at the focus 26 and arriving at thelines 53, which represent the connecting members 34 used in the systemof Fig. 3, are focused on the other ellipse focus 29 wherebycompensation for the distortion mentioned above is effected.

Referring to Fig. 5, reference numeral 54 denotes a zoned paraboloidalreflector comprising the three zones 55. 56 and 57 and attached to thesupporting member 58. The zones have a common axis 59 and a common pointfocus 60 and the adjacent zones are connected together through thecoaxial cylindrical members 61 which are similar in design to members34, Fig. 3. Reference numeral 62 denotes a radar transceiver which isconnected by the horizontal wave guide 63 through a coupling or gear box64 to the vertical guide 65 having an aperture or primary antenna 65facing reflector 54 and displaced from the focus 60. The coupler 64includes means for rotating the primary antenna about the focus 60. The

coupler may be of a conventional type or of the trammel type disclosedand claimed in the copending application of H. A. Baxter and W. D.Lewis, Serial No. 589,336, filed April 20, l945. This applicationmatured into United States Patent No. 2,541,324, granted February l3,1951.

In operation the waves are supplied from the transceiver 62 throughguide 63, coupler 64 and guide 65 to the rotating aperture 66. Theemitted waves are retlected by the zones 55, 56 and 57 and maximumaction occurs at an angle to axis 59. As the aperture 66 rotates aboutthe focus 60 the major lobe describes in space a cone having its axisaligned with the reflector axis 59; and conical scanning obtains. As thelobe rotates, its angular width at the half-power point remainsconstant. lts half-power width is relatively small and, in contrast toprior art wide angle conical scanning antennas, is not materiallydifferent from the half-power major lobe width obtained with theaperture 66 at the focus.

Referring to Fig. 6, reference numeral 67 denotes a zoned cylindricalparabolic reflector comprising the confocal zones 68, 69, 70 and 71, andattached to the supporting members 58. The zones have a common axis 72and a common focal line 73. Numerals 74 and 75 denote, respectively, atop conductive plate and a bottom conductive plate which are paralleland spaced in accordance with wave guide practice, a half or less of thedesign or mean operating wavelength. The plates 74, 75 are connected bythe semicylindrical or conductive side member 76 which forms with theplates a rectangular opening 77. Numerals 78 designate conductive flaresor horn sides attached to the longitudinal edges, and numerals 79designate end members attached to the short or transverse edges, of theopening 77. The bottom plate 75 contains a longitudinal slot 80 havingits axis included in the common latus rectum plane of the zones.

Reference numeral 81 denotes a right angle wave guide having an endaperture or primary antenna 82 facing reflector 67 and slidably mountedin slot 80. The wave guide 81 is connected through the coupler 83 andwave guide 63 to the translation device 62. The coupler 83 includesmeans for moving guide 81 back and forth along slot 80 and it may be ofa conventional type or of the trammel type disclosed and claimed in theaforementioned copending application.

The operation of the system of Fig. 6 is believed to be apparent in viewof the explanation given above in connection with Fig. 5. Assuming thefocal line 73 is vertical, as the reciprocating primary antenna 82 moveshorizontally, the major lobe oscillates in the horizontal plane over anangular sector related to the length of the slot 80. As discussedpreviously, the angular Width of the sector may be relatively great. Thehorizontal plane pattern of the major lobe is relatively narrow at thehalf-power point and its width remains constant during the scan. Thevertical plane pattern of the major lobe is wider at the half-powerpoint than the half-power width of the horizontal plane pattern. Withoutthe flares 78 the halfpower width in the electric or vertical plane isrelatively wide, and the flares function to decrease the vertical planewidth to a desired amount of say 5 degrees. Hence. the system of Fig. 6has a sharp horizontal plane major lobe pattern and a wide verticalplane major lobe pattern; and a so-called fan beam is secured.

Referring to Fig. 7, reference numeral 84 denotes a multiple zonereflector which was actually constituted and successfully tested. Thereflector comprises the twentyfour parabolic cylinders or zones denoted85 to 108. inclusive, and having a common axis 109. a common focal lineand a common latus rectum 111. Numeral 112 designates the aperture ofthe reflector 84. the aperture diameter being ten feet. The radius a ofthe outer circle 33 is six feet. A non-reflective member 48 and anelliptical reflective member (not illustrated) are included between eachpair of adjacent zones.

The different parabolic curves or contours of zones 85 to 108,inclusive, were ascertained by determining, in the case of each zone,the rectangular coordinates. as measured in inches, of several pointslying on the zone. More specifically, for convenience in measuring, theorigin of the axes was in effect transformed from the focus 110 to theintersection 113 of the XX axis and the circumference of the outercircle 33, and measurements were made from the new origin 113 along theXX1 axis and the YY axis. The relation between the X and X1 abscissasfor a point p on any zone is given by the following equation:

X =al=x+ (31) where t is the distance from the focus 110 to the point p.Using Equations 24, 25, 26, 27 and 31 the coordinates for the edges orextreme points and the intermediate points for each zone weredetermined. Thus, for the first or central zone 85 the coordinates forthe inner edge point 29, the outer edge point 28 and thirteenintermediate points were ascertained. By way of illustration, thecoordinates for the edges of the first zone 85, second zone 86, and thelast zone 108, and for several intermediate points spaced an inch aparton the second Zone 86, are given in the following table:

For a 50-degree scan, the primary antenna 35 was moved along the curvedpath 124 and positioned at the -20 and -25 positions 125 and 126. Thepath 124 is the arc of a circle having a radius of about ten feet and acenter four feet behind the vertex 29 which is approximately six feetfrom the focus 110.

The large multiple zone reflector 84, Fig. 7, was tested at the designfrequency corresponding to a wavelength of 3.415 centimeters and at twoother frequencies, one lower and one higher than the design frequencyand corresponding, respectively, to wave lengths of 3.440 and 3.362centimeters. In each test, a transmitter was connected to the directiveprimary antenna or horn 35 and the wave polarization was parallel to thefocal line 110. Also, in each test, for a 30-degree scan, the primaryantenna 35 was successively positioned at points 110, 120, 121 and 122,spaced degrees along the left or negative half of a linear path 123 andcorresponding to the 0, --5, and directions. The mid-point of paths 123and 124 coincide with the focus 110 and the total length of path 124subtends 50 degrees as measured from the vertex 29. With the born orfeed 35 at the focal position 110, that is, on the 0 direction theemitted waves are propagated in direction 127 along the axis 109 and thereflected waves are propagated in the opposite direction 128. For the 5,l0, 15, and positions of the horn 35. maximum action for the reflectedwaves occurs in the +5, +l0, +l5, +20 and +25 directions respectively,as shown by arrows 129, 130, 131. 132 and 133. Since the aperture ofreflector 84 is relatively large, namely ten feet, the gain is veryhigh.

Figs. 8, 9 and 10 illustrate the measured directive patterns taken inthe magnetic plane containing axis 109 and the path 123, 124 for hornand obtained during tests in which frequencies corresponding to theWavelengths 3.415. 3.440 and 3.362 centimeters respectively, wereemployed. In Fig. 8 reference numerals 134, 135, 136, 137, 138 and 139illustrate the separate and distinct patterns for the 0, +5, +10, +15",+20 and +25 antenna positions. In each pattern reference numeral 140denotes the major lobe, the line designated 141 represents the angularwidth of the lobe,as measured at the half-powerpoint and, except inpatterns 134 and 139, numeral 142 denotes the minor lobes. For patterns134 and 139 the minor lobe intensity was 20 decibels below the majorlobe intensity. It may be pointed out that, since the reflector 84 issymmetrical about axis 109, the directive patterns for the 5, l0, l5, 20and 25-degree positions are substantially the same as the directivecharacteristics 135. 136, 137, 138 and 139 for the +5, +10, +15, +20 and+25-degree positions, respectively.

Considering the patterns 134 to 139 inclusive, Fig. 8,

the half-power width 141 of the major lobe 140 in each pattern is about0.7. Hence scanning of a 50-degree sector (i25) is obtainable, withoutsubstantial change in the beam width, by moving the primary antenna 35along the path 124. The angular width of the sector is in the order ofseventy times the half-power width of the beam. By way of contrast, inprior art systems using a conventional parabolic reflector, the maximumsector width obtainable without materially increasing the lobe width, isordinarily only two or three times the lobe width. Also, in patterns to138 inclusive, the minor lobes 142 are of relatively low power ascompared to the minor lobes usually produced by parabolic reflectors ofthe prior art and are, therefore, negligible.

Referring to Figs. 9 and 10, reference numerals 143, 144, 145 and 146,Fig. 9, denote the magnetic plane patterns obtained at the 0, +5, +10and +15" horn positions, respectively, for the wavelength of 3.440 centimeters; and numerals 147, 148, 149 and 150 denote the patterns obtainedfor these horn positions for the wavelength of 3.362 centimeters. Thehalf-power widths 141 of the major lobes of patterns 143, 144, and 147,Fig. 9, and the half-power widths 141 of the major lobes 140 of patterns147, 148 and 149, Fig. 10, are substantially the same as the half-powerwidths 141 of the major lobes 140 of patterns 134, 135, 136, 137 and138, Fig. 8. The half-power width 141 in the 3.362 centimeter pattern150, Fig. 10, for the +l5 position is slightly greater than the widthsin the other patterns of Fig. 10. It is thus apparent from the patternsof Figs. 8, 9 and 10 that the zoned reflector of the invention performssatisfactorily over a band of wavelengths extending from 3.362 to 3.440centimeters. The band is a 2 per cent band and its mean wavelength isabout 0.6 per cent longer than the design wavelengths of 3.415centimeters.

In general, for a zoned parabolic cylindrical reflector, such as thereflector of Fig. 6 or Fig. 7, the half-power lobe or beam width, theangular width of the scanning sector or scannable field and the bandWidth may be determined approximately from the following equations:

2 where A: wavelength A=diarneter of reflector opening (aperture) r=radius of intermediate or mean circle A=maximum departure of zoneportions from mean circle It may be pointed out that heretofore, inorder to secure a narrow lobe, high directivity and eflicient scanning,in general, it has been necessary to utilize parabolic reflectors orpassive members disposed along a parabolic curve or surface and.considered from a mechanical or a size standpoint, the use of aparabolic system may not be advantageous. In accordance with the presentinvention, these desirable results may be secured by employing theprinciple of zoning and arranging the passive members along a curve orsurface which is not parabolic. In short, the principle of zoningeliminates the prior art limitation or necessity of using a parabolicstructure and permits a greater freedom in designing the system.

Although the invention has been explained in connection with certainembodiments it should be understood that it is not to be limited to theembodiments described inasmuch as other apparatus may be employed insuccessfully practicing the invention. In particular, zones havingsurfaces or contours other than parabolic may be use-'1. provided thecorresponding portions of the zone are disposed on the circumference ofa circle or a sphere. Also. other types of passive antenna members, suchas lens or wave guide apertures, may be employed as zone elementsinstead of the reflective elements described above; and the principle ofzoning is, in accordance with the invention,

equally applicable to so-called transmission gratings and reflectivesystems. In addition, the invention may be satisfactorily employed withwaves or radiant energy other than electromagnetic waves, as, forexample, light Waves.

What is claimed is:

1. An antenna system comprising a plurality of passive or secondaryantenna members spaced unevenly along an arc of a circle, an active orprimary antenna member positioned on a diameter of said circle, saidactive antenna being displaced from the center of said circle, and meansfor moving said active antenna.

2. An antenna reflector comprising a plurality of elliptical sectionshaving corresponding segmental portions located at spaced points on thecircumference of a circle and having a common focus coincident with thecenter of said circle.

3. An antenna reflector comprising a plurality of parabolic sectionshaving different focal lengths and a plurality of elliptical sections,one of said elliptical sections being included between each pair ofadjacent parabolic sections.

4. In combination, a zoned reflector comprising concave passive sectionshaving a common focus, one set of corresponding points of said sectionsbeing spaced on the circumference of a circle having its center at saidfocus, a transceiver, a primary antenna element connected to saidtransceiver and spaced from said focus.

5. In combination, a reflector comprising a plurality of coaxialconfocal parabolic sections having different focal lengths, themid-points of said sections being unevenly spaced on the circumferenceof a circle having its center at said focus a primary antenna elementconnected to a translation device and spaced from the axis of saidsections.

6. In combination, an antenna reflector comprising a plurality ofcoaxial confocal cylindrical parabolic sections having different focallengths and positioned on the circumference of a circle, a primaryantenna element connected to a translation device, and means connectedto said element for moving the element along the common latus rectum ofsaid sections.

7. In combination, an antenna reflector comprising a plurality ofcylindrical parabolic sections having a common focus and different focallengths, one set of corresponding segmental portions of said sectionsbeing spaced on one circumference and another set of correspondingsegmental portions being spaced on the other circumference of twoconcentric circles, a primary antenna element connected to a translationdevice, and means for oscillating said element along the common latusrectum of said sections and through said common focus.

8. In combination, a concave antenna reflector comprising a plurality ofparaboloidal sections having a common focal point and different focallengths, said sections being spaced on the surface of a sphere, aprimary antenna element connected to a translation device, and meansconnected to said element for moving said element about said point.

9. An antenna reflector comprising a plurality of confocal paraboliczones having inner edges positioned on one circumference and outer edgespositioned on the other circumference of two concentric circles, thecenter of said circles being coincident with the common focus of saidzones, the difference between the radii of said circles being a halfwavelength or an odd multiple, including the integer one, of a halfwavelength and the difference between the focal lengths of said zonesbeing a multiple, including the integer one, of a half wavelength.

10. In combination, a reflector comprising a plurality of coaxialconfocal parabolic sections having different focal lengths and spacedunevenly on the circumference of a circle, a primary antenna elementconnected to a translation device and included in the common focal planeof said sections, means connected to said element for moving saidelement in said plane relative to the common focus of said sections, theadjacent sections having focal lengths differing a multiple, includingthe integer one, of a half wavelength.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,504,017 Bailey Aug. 5, 1924 1,860,123 Yagi May 24, 19321,906,546 Darbord May 2, 1933 2,026,652 Ponte Jan. 7, 1936 2,253,50lBarrow Aug. 26, 1941 FOREIGN PATENTS Number Country Date 265,177 GreatBritain Dec. 22, 1927 770,482 France July 2, 1934 436,355 Great BritainOct. 9, 1935 635,293 Germany Sept. 14, 1936

